The present invention pertains to systems and methods for securely controlling access to information segments distributed to information receivers in a point-to-point or point-to-multi-point network. Such systems are known as conditional access systems. The information may include video, audio, text, data and any/or other type of information that may be subject to conditional access. An information segment is a given block of information, such as a television program, a given block of text or a given block of data, that typically is transmitted over a relatively short duration.
In the prior art, encrypted information segments respectively provided by a plurality of different conditional access information service providers are respectively encrypted for transmission in accordance with different conditional access processes, which may respectively utilize different algorithms for encrypting the information segments; and the differently encrypted information segments are respectively decrypted by differently configured information receivers respectively containing access control processors adapted for enabling decryption of only encrypted information segments encrypted in accordance with one of the different conditional access processes. An encryption algorithm is a process by which a given signal is processed with a key (signal) to transform the given signal into an encrypted signal that is unintelligible or by which the given signal can be recovered by corresponding processing of the encrypted signal with a corresponding key. The parameters of an encryption algorithm determine the order of selection for processing of bits in the given signal, the key and intermediate signals produced by such processing, and the sequence of such processing.
An exemplary prior art conditional access system is described in U.S. Pat. No. 4,631,901 to Klein S. Gilhousen, Charles F. Newby and Karl E. Moerder and U.S. Pat. No. 4,712,238 to Klein S. Gilhousen, Jerrold A. Heller, Michael V. Harding and Robert D. Blakeney. In such conditional access system, an information segment is encrypted for transmission by scrambling the information segment with a keystream that is produced by processing a secure session key in accordance with a predetermined encryption algorithm, such as the DES encryption algorithm. In an information receiver of such a conditional access system, the encrypted information signal is decrypted by descrambling the encrypted information segment with a keystream that is produced by processing the secure session key in accordance with the predetermined encryption algorithm. The session key is a key that is processed to produce the keystream that is used to scramble an information segment for a given transmission of the encrypted information segment. Typically the session key is processed with another key and/or a data signal to produce the keystream. In the two above-cited patents, the session key is referred to as a channel key.